If there is one candle color you'd never want to be without, it would be your white candles. These can be subbed for any other color, when you find you don't have the "right" color on hand. There is never a wrong place or wrong time for this color. These are the best choice for an "all purpose" candle.
White candles bring about a sense of peace and calm. They quiet the mind, and give you space to explore your emotions without being overwhelmed by them. Burn white candles for meditation or divination. They bring about clarity, and will help you find the truth.
White candles convey a sense of innocence. Burn them in cleansing or purifying rituals. They can be used to symbolize fresh starts, when possibilities stretch out endlessly before you and the future is a blank slate.
White candles are particularly associated with the element of Spirit.
How should I charge my candles? When you are ready to use your candle, before you light it, take a moment to simply hold it in your hands and focus on your objective. In addition to the general intention, think about your situation in particular, and the change that you would like to create. Some people choose to anoint their candles with oil at this time, or carve symbols into the wax. That's entirely up to you.
Why should I trim my candle wick? The length of a candle's wick determines how much fuel (the melted wax) is feeding the flame. If the wick is left too long, the candle burns more quickly than it should. It also produces more soot as it burns, which can leave a residue on the walls and ceiling. If the wick is too short, the candle will not stay lit. The ideal length is between 1/8-1/4".